CEA is a heat stable glycoprotein having an isoelectric point at pH 4.5, a carbohydrate content of about 40-75% by weight, a high N-acetylglucosamine content (10-30% by weight), a trace of N-acetylgalactosamine and about from 4-20% by weight sialic acid. It is prepared by known methods from tumors or tissue culture. CEA is significant because elevated serum CEA concentrations have been associated with certain cancers, particularly those of the gastrointestinal tract. CEA tracers (labelled CEA analogues), CEA antibody and labelled CEA antibody are all known (U.S. Pat. Nos. 3,663,684 and 3,927,193).
.alpha..sub.1 acid glycoprotein or orosomucoid (hereinafter AG) is heat stable and contains about 40-45% by weight carbohydrate, about 10% by weight sialic acid and aspartic acid, glutamic acid, methionine, N-acetylglucosamine and N-acetylgalactosamine in similar concentration to that in CEA. AG differs substantially from CEA in having an isoelectric point at pH 2.7, .alpha.-globulin electrophoretic mobility rather than .beta.-globulin mobility and a molecular weight of about 45,000 rather than the approximately 200,000 of CEA. Insolubilized AG is known in the prior art. While various substances present in normal tissue are known which immunologically cross-react with CEA (nonspecific cross-reacting antigens or NCA), these substances have not been identified as having AG immune determinants.
It is an object of this invention to improve the sensitivity of known CEA assays and to provide a novel reagent for this purpose.
Another object of this invention is to provide a novel method and reagent for determining CEA.
A further object is to develop a novel method for screening the body fluids of cancer patients for cancer-associated substances that have diagnostic significance for cancer.
These and other objects will be apparent from consideration of the specification as a whole.